How do you change pencil tool automation depth?

[duderonomi]

I have drawn triangle volume automation, on a eighth note grid, on an electric guitar track. My question is how can I change the depth of the triangles to minutely tweak the vibrato without having to redraw the automation to try and get close to the depth I am looking for.

I have highlighted the automation and used the trimmer tool to try and do this but it is lowering the whole automation volume keeping the drawn depth. I want to change the depth but keep the initial volume where it is.

Thanks in advance.